Variable inductance device



1949. w. L. ATWOOD 2,461,804

VARIABLE INDUCTANCE DEVICE Filed Sept. 18, 1945 2 Sheets-Sheet l /6 ma I IN VEN TOR. lV/L FR/D L /47'IV000 ATTORNEY Feb. 15, 1949. w. L. ATWOOD VARIABLE INDUCTANCE DEVICE 2 Sheets-Sheet 2 Filed Sept. 18, 1945 Tiara INVENTOR. lfiLFR/D L /47'l(/000 ATTORNEY Patented Feb. 15, 1949 UNITED VARIABLE INDUL'IANOE DEVICE Wilfrid L. Atwood, Newton Lower Falls, Mala, assignor to The Girdler Corporation, Louisville, Ky., a corporation of Delaware Application September 18, 1945, Serial No. 617,029

3 Claims. (Cl. l'l1242) This invention relates to variable inductance devices such as high-frequency high-power tuning coils and has for an object the provision of a coil of high electrical efliciency, of rugged relable mechanical design, and smoothly adjustable over a wide range of inductance values.

Heretoiore, helical tuning coils have been proposed in which the turns of the coil have served as threads in order to advance bridge arms or contact devices lengthwise of the coils. The mounting of these movable contact members has presented considerable difliculty because they must not only be free for axial movement, but

they must also have freedom of movement in other directions. They must maintain a good electrical contact at all times. This is important from the standpoint of preventing undue heating. If poor contacts are present, arcing and burning effects may appear which may seriously injure or abrade the conductors and thereby render diiiicult or prevent subsequent adjustment or tuning oi the coil.

In carrying out the present invention in one form thereof, a helical coil is mounted from suitable insulating supports with a conductor extending therethrough adjacent the turns and parallel to the axis thereof. Means are provided to rotate this conductor about the axis 01 the coil. A relatively long bearing member, freely slidable on said conductor, slidably supports a cradle, between two rollers of which there is provided a contact member for completing a connection from said conductor to a turn of the coil. The rollers partly encircle the engaged turn of the coil to guide the contact member and to propei the cradle and bearing member lengthwise oi the coil upon rotation of said conductor. The arrangement is reliable and satisfactory with a relatively long life of useful operation.

For a more complete understanding of the invention and for further objects and advantages thereof, reference is now to be had to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a treat elevation of a tuning coil embodying the invention with certain parts cut away to show the movable contact assembly;

Fig. 2 is a sectional view taken on the line 22 of Fig. 1;

Fig. 3 is an enlarged plan view of the movable contact assembly and cradle;

Fig. 4 is a sectional view taken on the line 4-4 of Pig. 3; and

Fig. 5 is a sectional view taken on the line 5-8 0! H8. 3.

Referring to the drawing, the invention has been shown in one form as applied to a helical tuning coil in formed from a tubular conductor of substantial size, that is, of the order of from one to two inches or more in diameter. The coil is supported from a frame ll, of hardwood or other material, by means of two rows, i2 and ll, of insulators respectively carrying lugs at their upper ends which are suitably secured, as by silver soldering, to the turns of the coil II. To one end of the coil there extends an input conductor l5. With the parts in the illustrated positions, the circuit includes approximately five turns of the coil ll, since a movable contact l6 completes the circuit from the turn Illa through a cradle i! and contact It to a horizontal conductor II. The circuit may be further traced through an arm 2| to a horizontal conductor 2i against which a contact 22 has a sliding and wiping engagement. The horizontal conductor 21 is supported coaxially of the coil It by a journal 23 and has secured to it an insulator 2d driven by a sprocket 25, a chain 26, and a driving sprocket 21 mounted on a shaft 28. The latter may be driven by any suitable means, such as a hand-crank or a motor. The journal 23 is also mounted on insulators lid.

The disposition of the conductor i9 adjacent the turns and lengthwise of the coil ill is made possible by the spacing and driving arm 20. A similar arm 30 is connected to the opposite end of conductor i9 and to a conductor 3i supported by a journal 32 for rotation about the axis of the coil lb, The journal 32 is also supported by insulators l3a, corresponding and in alignment with those shown in Fig. 2 for the coil 10. In effect there is provided a double crank, the conductor i9 being common to both. in accordance with this arrangement the supporting and driving means for the contact l6 may be disposed quite new it.

To minimize opposition to movement and to insure the smooth operation essential to precise adjustments, there is provided the cradle ll which it will be observed is relatively long. It has a length equal to the distance between three turns of the coil. The relatively long bearing suriace provided by the cradle ll insures easy and smooth movement along conductor l9 without tendency for the ends to dig into its surface. The contacts i6, i8 and 22 each comprise a plurality of flexible, elastic fingers which resiliently engage and wipe their associated conductors to insure good low-resistance electrical contact therewith. The contact is has resilient fingers of lengths which increase, Figs. 2, 3 and 5, irom the mid-portion of a turn toward the inside thereof, and in general conform to the configuration of the turn.

As best shown in Fig. 5, the cradle i1 telescopically supports the contact assembly. A cylindrical extension slidably carries a cup-shaped member 36 having a skirt 360 within which is disposed a compression spring 37. The latter bears against the closed end of the member 36 and against the cradle ll. Good electrical contact is insured between them by the circular array of contact fingers 38.

The member 36 has a pair of flanges 39 and 40 to which there is secured roller-supporting plates 4| and 42 as by screws 43 and 44. Rollers 45 and 46 are journaled at the respective ends of the plates 4| and 42, shafts 41 and 48 with nuts on their threaded ends being provided for that purpose.

In Fig. 2, it is to be observed that the rollers 45 and 46 are disposed on opposite sides of theresilient contact member I 6. They not only guide the contact member IS in its movement around each turn of the coil but they also partially encircle the conductor of each turn, as the turn Illa, to apply to the plates a force which is transmitted to the bearin member or cradle I! to propel it along conductor I9.

Irregularities in the diameter of the conductor are taken care of by the resilient contact fingers i6. Variations in the diameter of the helix are taken up by the telescopic movement of the contact assembly relative to the cradle IT. The fingers l6 also take care of irregularities in the spacing of the turns or their departure from a true helix. Thus, there is provided limited freedom of movement in all directions to the end that the conductor l9 may be rotated easily and smoothly to adjust the inductance or the number of turns of the coil included between input conductor l5 and the output contact 22. Obviously, both ends of the coil may be connected to input or output conductors and the contact 22 may serve as either an input or an output conductor.

By reason of the foregoing features including the double crank, the forces applied to the contact assembly to move it are almost tangential to it. They are not applied through an arm pivoted at the axis of the coil. The force or torque applied by the conductor 19 is transmitted through the cradle ll in a direction at right angles to the axis along which it is movable and in a direction substantially tangential to that part of the coil engaged by the contact IS. The described arrangement has in practice been found to be quite satisfactory.

What is claimed is:

1 A variable inductance device comprising a conductor wound in the form of a helix, a second conductor, means adjacent the ends of said coiled conductor for pivotally supporting said second conductor for rotation about the axis of said helix, said second conductor including arms extending from said axis toward said helix and a straight section extending parallel to the axis, and adjacent the turns, of said helix, a bearing member freely rotatable and slidably supported on said straight section and having a circular array of resilient contact members bearin upon and surrounding said straight section to provide circumferentially thereof a low-resistance electrical connection, means forming a slidable electrical connection between said bearing member and a turn of said helix, and rollers supported from said bearing member and disposed on opposite sides of said electrical connection for guiding and propelling said bearing member along said straight section upon rotation of said second conductor.

2. A variable inductance coil having a plurality of turns forming a helix, contact means forming a wiping engagement with a turn of said helix, means for moving said contact means circumferentially around and along said turns comprising a conductor extending adjacent the turns, and parallel to the axis, of said helix, means connected to said conductor for supporting and rotating it about the axis of said helix, a relatively long bearing member freely rotatable and slidably mounted on said conductor and having a circulararray of resilient contact members bearing upon and surrounding said conductor to provide circumferentially thereof a low-resistance electrical connection, a cradle slidably supported from said bearing member for supporting said contact means, and rollers supported from said cradle on opposite sides of said contact means for propelling the latter and said cradle lengthwise of said helix upon rotation of said conductor, said rollers having their engaging surfaces curved partially to encircle each turn of said helix.

3. A variable inductance device comprising a conductor formed into a helical coil, a second conductor extending through said coil, parallel to the axis of said coil, in spaced relation therewith and adjacent the turns of said coil, means located adjacent the respective ends of said coil and forming a double crank with said second conductor for rotatin it about the axis of said coil, a relatively long cradle rotatably slidably carried by said second conductor and having a circular array of resilient contact members bearing upon and surrounding said second conductor to provide circumferentially thereof a low-resistance electrical connection, a contact assembly telescopically supported from said cradle and in driving relation therewith, said assembly comprising resilient contact fingers of variable length together disposed in partial encirclement of a turn of said coil, side plates extending on opposite sides of said contact fingers, a concave roller carried at each of the respective ends of said plates and disposed in partial encircling relation to a turn of said coil for propelling said cradle along said second conductor and to minimize transmission of forces through said contact fingers, and a spring between said cradle and said contact assembly to provide additional freedom of movement therebetween.

WILFRID L. ATWOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,845,406 Gebhard Feb, 16, 1932 2,163,645 Ware June 27, 1939 2,324,189 Bock July 13, 1943 2,425,411 Zottu Aug. 12, 1947 

